Low-melting copolyamide and their use as hot-melt adhesives

ABSTRACT

Copolyamides, consisting of polycondensation products of the following components: caprolactam 10 to 45 mol-%, laurolactam 30 to 55 mol-%, at least 2 dicarboxylic acids 20 to 50 mol-% of the following compounds, aliphatic α,ω-dicarboxylic acids with 6 up to 14 C atoms inclusively, terephthalic acid, isophthalic acid and 2,6-naphthalene dicarboxylic acid, wherein the content of aromatic dicarboxylic acids is lower than 10 mol-%, with reference to the allover amount of the above-mentioned components, which add up to 100 mol-%, a diamine mixture in an amount that is equimolar to that of the dicarboxylic acids, chosen from the group of the following substances, hexamethylene diamine, piperazine and/or 2-methyl- 1,5-diaminopentane, wherein the molar content of hexa-methylene diamine is between 75 and 95 mol-% with reference to the diamine mixture.  
     The copolyamides according to the invention are used for the production of mono- and multifilaments, fibers, films and nets.

BACKGROUND OF THE INVENTION

[0001] Hot-melt adhesives on the basis of aliphatic copolyamides for theproduction of bonds between interlining textiles and face fabrics whichare resistant to washing and dry cleaning have been known for a longtime and are extensively used on a world-wide scale. Such polyamides arefor instance disclosed in DE-A 1594233. The desired temperatures of themolten mass of between 80 and 130° C. are adjusted by the additionalcombination of further ω-amino carboxylic acids and further polyamideformers like 6,6 salt, 6,9 salt, 6,10 salt and/or 6,12 salt in differentamounts with the commonly used components caprolactam/ω-aminocapronicacid and laurolactam/ω-aminolauric acid.

[0002] The stickiness or adhesive power of the known polyamides in amolten state is sufficient to permit their use in the hot-melt sealingand bonding of textiles in the textile industry. They also show a goodresistance to the solvents generally used in the dry cleaning oftextiles and to the washing temperatures of up to approximately 80° C.generally used in the textile industry. This resistance greatly dependson a high content of laurolactam and/or 11-aminoundecanenic acid ordimer fatty acid, though. The higher the content of these basiccomponents, the higher the resistance to high washing temperatures; butsimultaneously, the melting temperature of the copolyamides also rises,which is not desirable. Therefore, the known copolyamides cannot be usedfor the hot-melt sealing of temperature-sensitive substrates likeleather, temperature-sensitive fleeces, felts, velvet finishes and thelike made of natural or synthetic fibers. In DE-A 2324160 and DE-A2324159 a copolyamide containing great amounts of caprolactam and havinga low melting temperature of below 115° C. was suggested as the solutionto this problem. This copolyamide must contain 20 to 40 wt.-%caprolactam. This copolyamide is suitable for the holt-melt sealing oftemperature-sensitive substrates and has good adhesive properties and ahigh resistance to dry cleaning agents despite low bonding temperatures.However, it is a drawback that the lower melting point results in alower resistance to washing. This is confirmed by German Patent DE 37 30504.

[0003] Practical work has shown that in order to reach a low meltingpoint, the polyamide must contain at least two dicarboxylic acids ascomponents, wherein part of the usual aliphatic dicarboxylic acids maybe substituted by aromatic compounds. However, the proportion ofaromatic diacid(s) must not be greater than 10 mol-% (in reference tothe total amount of the formulation), as a further increase in thecontent of aromatic compounds results in products with a highglass-transition temperature (Tg), which do not crystallize any more andremain completely amorphous. Such substances are mostly unsuitable ashot-melt adhesives, since they display a bad resistance to washing anddry cleaning.

[0004] On the other hand, many applications also require the hot-meltadhesive to remain workable for some time after application. This isoften the case in direct laminating, where a certain time elapsesbetween the application of the adhesive and the laminating and theadhesive should not lose its adhesive properties in the meantime.

[0005] The time-span within which the adhesive displays its adhesiveproperties is also often called “open time” among those skilled in theart.

[0006] According to the definition by ASTM Standard D 4497-85 the opentime corresponds to the time available between the application of theadhesive on the first substrate and the bonding with the secondsubstrate, wherein the force required for separating the layers againmust still amount to 50% of the overall value.

[0007] Classic ternary copolyamides and their uses as hot-melt adhesivesare described in DE-A 2204492. These substances show rather good textileproperties regarding resistance to washing and dry cleaning, but theyhave the disadvantage of a relatively high melting point, which rulesout fabric-protecting, energy-saving bonding.

[0008] The German patents DE 2324159 and DE 2324160 describe low-meltingcopolyamides. However, due to the low melting point, these have areduced resistance to washing.

[0009] Also in the German laid open application DE-A 3248776 low-meltingcopolyamides are described. These are especially suitable for bondingwith siliconized outer textiles and contain C₆₋₁₂ diamines in additionto lactams and C₆₋₁₂ dicarboxylic acids, wherein at least 30% of thesediamines consist of single-branched aliphatic diamines with 6 carbonatoms.

[0010] Further hot-melt adhesives with a clearly higher content ofadditional diamines (in addition to hexamethylene diamine) are alsodescribed in the literature. Thus DE-A 2509791 mentions copolyamideswith at least 70 mol-% diamines with at least one secondary amino group.

[0011] The copolyamides described there are above all used in thefurniture industry for the veneering of edges.

[0012] Finally, the European patent EP 0 965 627 describes copolyamideswith a very long open time. However, the compounds described there donot offer any resistance to dry cleaning.

[0013] It is therefore the object of the present invention to providenew low-melting copolyamides which can be used as hot-melt adhesives anddisplay a good resistance to washing and dry cleaning and have aprolonged open time.

BRIEF SUMMARY OF THE INVENTION

[0014] The present invention relates to novel low-melting copolyamidesconsisting of at least six components, which can be preferably used ashot-melt adhesives for textiles and for technical applications.

DETAILED DESCRIPTION

[0015] This object is solved by the copolyamides according to claim 1and their uses according to claims 8 and 9.

[0016] The subclaims contain advantageous embodiments of the invention.

[0017] The subject of the invention are copolyamides with the followingcontents: caprolactam 10 to 45 mol-% laurolactam and/or12-aminododecanenic acid 30 to 55 mol-% at least 2 dicarboxylic acids 20to 50 mol-%

[0018] of the following compounds:

[0019] aliphatic α,ω-dicarboxylic acids with 6 to 14 carbon atomsinclusively, terepthalic acid, isophthalic acid and 2,6-naphthalenecarboxylic acid, wherein the content of aromatic dicarboxylic acids islower than 10 mol-%, in reference to the allover amount of theabove-mentioned components adding up to a total of 100 mol-%,

[0020] an amount of a diamine mixture equimolar to that of thedicarboxylic acids, chosen from the group of the following substances:

[0021] hexamethylene diamine, piperazine and/or2-methyl-1,5-diaminopentane, wherein the molar content of hexamethylenediamine in reference to the diamine mixture amounts to between 75 and 95mol-%.

[0022] In addition to the above-mentioned components, the hot-meltadhesives according to the present invention may also contain usualstabilizers and chain regulators for the adjustment of viscosity. Suchadditives are known to the skilled person.

[0023] The copolyamides according to the present invention display thefollowing features:

[0024] low melting point enabling a fabric-protecting and energy-savingbonding,

[0025] very high resistance to dry cleaning,

[0026] very high resistance to washing,

[0027] long open time and therefore good bonding properties also intechnical applications.

[0028] This prolongation of the open time is obtained in the case of thehot-melt adhesives of the present invention by the use of at least oneadditional diamine in addition to hexamethylene diamine. If smallamounts of piperazine and/or 2-methylpentamethylene diamine(2-methyl-1,5-diaminopentane) are polymerized into the polymer, productswith a greater longevity of their adhesive properties will be obtained.If piperazine is added, the effect even seems to be a little stronger.

[0029] The most surprising discovery is that the properties are greatlyimproved through the addition of small amounts of piperazine and/or2-methyl-1,5-diaminopentane in addition to hexamethylene diamine. It wasfound that up to a maximum content of 25 mol-% referring to the diaminemixture, it is not only possible to prolong the open time, but also theresistance.

[0030] Surprisingly, this beneficial effect is diminished again if thecontent of piperazine and/or 2-methylpentamethylene diamine(2-methyl-1,5-diaminopentane) in the formulation is raised too high.

[0031] The use of piperazine as a component of copolyamides used ashot-melt adhesives is known as such.

[0032] German Patents DE 3730504 and DE 19512004 explicitly mentioncopolyamides with piperazine as a monomer. The amount of piperazine usedin the copolyamides described there is much higher, however, and thecopolyamides claimed are characterized by a rapid hardening orcrystallization of the hot-melt adhesive, which means that the open timeis very short.

[0033] Therefore, the copolyamides of the present invention as describedhere have the advantage of the long open time as compared to thesubstances available in the state of the art. Furthermore, they are alsomore cost-effective due to the lower concentration of additionaldiamines.

[0034] The 2-methyl-1,5-diaminopentane used is a commercially availablemixture of isomers (the product Dytek® by DUPONT company) containing2-ethyl-1,4-diaminobutane as a side product.

[0035] The polyamides of the present invention are produced according toknown processes, whereby the production process may be continuous ordiscontinuous. All components are statistically bonded to the polymer.

[0036] As already mentioned above, the open time is of decisiveimportance above all in technical bonding processes, in which theadhesive should be active for a certain time.

[0037] The copolyamides described show such a behavior.

[0038] Due to their properties, the substances can preferably be used ashot-melt adhesives in the form of granules or powder, but their adhesiveproperties can also be used in films, nets, fibers or filaments producedfrom the polymer.

EXAMPLES

[0039] The statistical copolyamides listed below were synthesizedthrough hydrolytic polycondensation of the individual monomercomponents. monomers example example Example comparative comparativecomparative [mol-%] A B C example 1 example 2 example 3 caprolactam 3025 27 30 30 40 laurolactam 40 50 40 50 40 40 adipic acid 10 — 3 — — 20azelaic acid 10 — 11 — 15 — sebacic acid 10 19 10 — 15 — dodecane diacid— — — 20 — — terephthalic acid — 6 9 — — — hexamethylene 25 20 25 — — 20diamine piperazine 5 — — 20 — — 2-methylpentane — 5 8 — 30 — diaminerelative viscosity 1.37 1.36 1.34 1.41 1.38 1.35 (0.5% in m-cresol)melting point/[° C.] 104 100 79 113 109 121 (according to DIN 53765)

[0040] For the analysis of their technical application properties thepolymers were ground by means of a commercially available cold grindingdevice.

[0041] The fraction of 80 to 200 μm was sieved off and used forpowder-dot coatings with a CP-52 engraved printing roller.

[0042] The coating was applied on a cotton interlining fabric.

[0043] The coating weight was adjusted to 13±1 g per square meter.

[0044] The samples were pressed together with the following face fabricsat temperatures of between 100 and 130° C.: PES/Wo 55/45 (polyester-woolblend (55/45 w/w%).

[0045] In order to measure the adhesion strength on textiles, thusbonded together textile strips of a width of 5 cm were mounted in atraction machine.

[0046] The examination parameters remained the same in all measurementstaken: test speed: 100 mm/min width of the test object:  50 mm testpath:  80 mm bias force:  0N test temperature:  25° C.

[0047] The following table shows the adhesion forces for thecopolyamides A to C produced according to the invention and those of thecomparative examples 1 to 3.

[0048] The annotations therein mean the following:

[0049] OB: original bonding

[0050] 40° C.: adhesion after washing at 40° C.

[0051] DC: adhesion after dry cleaning

[0052] T: bonding temperature

[0053] Unit used for the separation force of the individual copolyamideson polyester/wool: [N/5 cm] [N/5 cm] A B C 1 2 3 T = 100° C. OB 6.5 7.810 3.0 3.5 0.5 40° C. 5.5 6.9 7.0 1.3 1.4 0 DC 6.3 7.5 9.0 2.0 2.0 0 T=110° C. OB 8.5 10 13.5 4.5 6.8 1.9 40° C. 7.7 9.4 11.0 2.8 4.4 0 DC 8.59.5 12.5 4.0 6.0 0.5 T = 120° C. OB 11 13 16 7.5 10 4.0 40° C. 9.5 11 135.0 7.5 1.9 DC 10 13 14.5 6.0 8.1 2.5 T = 130° C. OB 13 15 18 10 13 7.540° C. 11 13 16 8.2 9.6 5.0 DC 13 14 16.5 9.1 11 5.0

[0054] The open time was measured according to ASTM D 4497-85.

[0055] As the first substrate a dense PES knitted fabric was used; asthe second substrate a pure wool fabric was used.

[0056] Measurements were taken at 140° C. and at 170° C.

[0057] The load used was 100 g.

[0058] Open time according to ASTM D 4497-85 A B C 1 2 3 T = 140° C.open time/[s] 60 50 60 10 120 20 thickness of layer/[μm] 520 600 550 610540 570 T =170° C. open time/[s] 70 50 70 20 30 20 thickness oflayer/[μm] 70 520 530 480 490 580

[0059] Although the present invention has been described with referenceto preferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. Copolyamides, consisting of polycondensation products of thefollowing components: caprolactam 10 to 45 mol-% laurolactam 30 to 55mol-% at least 2 dicarboxylic acids 20 to 50 mol-%

of the following compounds: aliphatic α,ω-dicarboxylic acids with 6 upto 14 C atoms inclusively, terephthalic acid, isophthalic acid and2,6-naphthalene dicarboxylic acid, wherein the content of aromaticdicarboxylic acids is lower than 10 mol-%, with reference to the alloveramount of the above-mentioned components, which add up to 100 mol-%, adiamine mixture in an amount that is equimolar to that of thedicarboxylic acids, chosen from the group of the following substances:hexamethylene diamine, piperazine and/or 2-methyl-1,5-diaminopentane,wherein the molar content of hexamethylene diamine is between 75 and 95mol-% with reference to the diamine mixture.
 2. Copolyamides accordingto claim 1, characterized in that the monomers are present in thefollowing molar relations: caprolactam 15 to 40 mol-% laurolactam and/or12-amino dodecanenic acid 30 to 45 mol-% at least 2 dicarboxylic acids20 to 40 mol-%

of the following compounds: aliphatic α,ω-dicarboxylic acids with 6 to14 C atoms inclusively, terephthalic acid, isophthalic acid and2,6-naphthalene dicarboxylic acid, wherein the content of aromaticdicarboxylic acids is lower than 10 mol-%, with reference to the alloveramount of the above-mentioned components, which add up to 100 mol-%, adiamine mixture in an amount that is equimolar to that of thedicarboxylic acids, chosen from the group of the following substances:hexamethylene diamine, piperazine and/or 2-methyl-1,5-diaminopentane,wherein the molar content of hexamethylene diamine is between 80 and 95mol-% with reference to the diamine mixture.
 3. Copolyamides accordingto claim 1, characterized in that the monomers are present in thefollowing molar relations: caprolactam 15 to 40 mol-% laurolactam and/or12-amino dodecanenic acid 30 to 45 mol-% at least 2 dicarboxylic acids20 to 40 mol-%

of the following compounds: aliphatic α,ω-dicarboxylic acids with 6 to14 C atoms inclusively, terephthalic acid, isophthalic acid and2,6-naphthalene dicarboxylic acid, wherein the content of aromaticdicarboxylic acids is lower than 10 mol-%, with reference to the alloveramount of the above-mentioned components, which add up to 100 mol-%, adiamine mixture in an amount that is equimolar to that of thedicarboxylic acids, consisting of the substances hexamethylene diamineand piperazine, wherein the molar content of hexamethylene diamine isbetween 75 and 95 mol-% with reference to the diamine mixture. 4.Copolyamides according to claims 1 to 3, characterized in that themelting point of the copolyamides measured in accordance with DIN 53765is lower than 120° C. (peak maximum).
 5. Copolyamides according toclaims 1 to 3, characterized in that the melting point of thecopolyamides measured in accordance with DIN 53765 is lower than 100° C.(peak maximum).
 6. Copolyamides according to claims 1 to 3,characterized in that the melting point of the copolyamides measured inaccordance with DIN 53765 is lower than 90° C. (peak maximum). 7.Copolyamides according to one of the preceding claims, characterized inthat the 2-methyl-1,5-diaminopentane used is a mixture of isomers, whichcontains 2-ethyl-1,4-diaminobutane as a side product.
 8. The use ofcopolyamides according to claims 1 to 7 as hot-melt adhesives.
 9. Theuse of copolyamides according to claims 1 to 3 for the production ofmono- and multi-filaments, fibers, films and nets.